A motor car has to function as a product of good engineering while in most cases also being aesthetically pleasing. There is often a conflict of interest between designers and aerodynamicists when deciding on the form of the vehicle. With high speed motor cars, such as those capable of exceeding 200 or even 300 kilometres per hour, lift can be generated in the region of the rear “axle” area and such fast motor cars require a low co-efficient of lift to prevent them from losing grip in corners and so as to avoid undesirable driving characteristics.
It is also desirable for a motor car to have relatively low drag so that it is economical and/or can travel faster with a motor/engine providing a given power to the power train.
One aerodynamic device used is a rear “flip”. Some of the earliest effective motor cars to use these devices were the Ferrari 250 GTO, and the Aston Martin DP214 and DP215 racing cars which in the year 1963 where the first motor cars ever to be officially timed at over 300 kph on the very long Mulsanne Straight at Le Mans. More recently, boot lid flips have become relatively common among production cars and are included on, for example, the Aston Martin DBS, BMW Z4 and Mercedes Benz SLK55 AMG models.
Another aerodynamic device is a deployable spoiler such as used on the Bugatti Veyron Super Sport at the rear of the vehicle. Another known aerodynamic device is a fixed wing at the rear of the vehicle such as used on the Aston Martin V12 Zagato and Mercedes Benz C63 AMG Black Series models. Another aerodynamic device is a Gurney flap which is an element which may be fixed to the top trailing edge of a wing on a racing car and has been used since the 1970s.
FR-A-2885343 discloses the use of blowing slots on an MPV or hatchback with a flat roof. EP-A-1506911 shows air blown out near a rear windscreen of a hatchback. EP-A-1907267 shows a motor car having a horizontal opening for air which has passed a cooling duct. EP-A-1048556 shows an apparatus for emitting air up next to and behind a substantially vertical drop surface behind a substantially horizontal boot lid—a rather unsightly arrangement due to the exterior nature of the apparatus. EP-A-0467523 discloses air passageways inclined upwards and with baffles disposes in the passageways.
While some of these devices can be useful to greater or lesser extents from an aerodynamic performance perspective, they do not always fit in with the objects which vehicle designers may be attempting to achieve from an aesthetic perspective on some projects. Some vehicle designers may desire very clean lines for the shape of their vehicles, at least when the vehicles are on display or stationary and without a substantial and/or complex arrangements. It is very challenging to engineer a vehicle which is capable of very high speed with good vehicle response and stability across the road speed range during straight line and cornering manoeuvres while also meeting vehicle aesthetic design objectives.